1. Field of Invention
This invention relates generally to a variable microwave phase shifter using ferroelectric material and high temperature superconducting material to implement variable phase shifting while maintaining relatively low power losses.
2. Discussion
Variable time delay lines or phase shifters are utilized in a wide variety of electronic devices for controlling the phase relationships of signals. One electronic device, a phased array antenna, relies heavily on phase shifters. The phased array antenna generally includes a planar array of radiating elements in an associated array of phase shifters. The radiating elements generate a beam having a planar wave front, and the phase shifters vary the phase front of the beam to control its direction and shape. A typical phased-array antenna may have several thousand elements with a phase shifter for every antenna element. Accordingly, low cost, high reliability, and low complexity of the phase shifters are important design considerations.
Phase shifters may generally be grouped into one of two categories. One category of phase shifter utilizes the variable permeability of ferrites to control the phase shift signals. This type of phase shifter typically includes a thin ferrite rod centered within a rectangular waveguide. A magnetic field applied to the ferrite rod by an induction coil wrapped around the waveguide varies permeability of the ferrite rod, thus controlling the propagation speed, or the phase shift, of signals carried by the waveguide. A second type of phase shifter utilizes varying signal path links to control the phase shift of signals propagating therethrough. Such phase shifters generally include a bank of diodes and various lengths of conductors switched into or out of the signal path by the diodes in order to vary the propagation time or phase shift of signals propagating through the conductors.
U.S. Pat. No. 5,153,171 covers a superconducting variable phase shifter which employs superconducting quantum interference devices (SQUID's) connected in parallel with and distributed along the length of the transmission line. Direct current (DC) control current varies the inductance of the individual SQUID's, thereby distributing inductance of the transmission line in order to control the propagation speed or phase shift of signals carried by the transmission line. The superconducting variable phase shifter provides continuously variable time delay or phase delay over a wide signal band width with relatively low insertion losses and power consumption. However, this apparatus uses superconducting quantum interference devices connected in parallel which requires fabrication of a number of such devices.
Soviet reference SU 1193-738 discusses a microwave phase shifting network having a first gap at least two times larger than a second gap and a complimentary transmission line arrangement. The phase shifter shown in the Soviet reference relies on the superposition of two leaky waves within the gaps in order to generate the phase shift. The Soviet reference, however, fails to take advantage of a co-planer waveguide transmission line structure which controls the propagation velocity in accordance with both the geometry and the dielectric properties of the co-planer waveguide.